METHOD AND APPARATUS FOR PRODUCING IRON

Abstract: Method and apparatus for producing iron by melt reduction of concentrate or prereduced concentrate in a melt bath in a reactor, e.g. a converter (10). Concentrate and carbonaceous reducing agent are supplied to the melt bath consisting of a layer (28) of molten iron and a layer (30) of slag floating thereon. Oxygen-containing gas, such as hot air, is blown by blowpipes (38) into a so-called post-combustion zone (37) towards the slag layer so as to combust the reducing gases being discharged and to heat the melt bath. The hot exhaust gases produced in the combustion process are led out through an outlet (12) in the roof of the reactor. The oxygen-containing gas is blown into a post-combustion zone shielded from the walls of the reactor by cooling panels (42) so as to prevent the slag and metal drops splashing up during the blowing from reaching the uncooled walls (11) of the reactor in the gas phase.

Description: METHOD AND APPARATUS FOR PRODUCING IRON The present invention relates to a method and an apparatus for producing iron by melt reduction of concentrate or prereduced concentrate in a melt bath in a reactor, e.g. a converter, wherein concentrate or prereduced and partially molten concentrate and carbonaceous reducing agent, such as coal, is supplied to the melt bath consisting of a layer of molten iron and a layer of slag floating thereon; oxygen-containing gas, such as hot air, is blown into a so-called post-combustion zone by means of blowpipes towards the slag layer in order to bring about combustion of the reduction gases being discharged so as to heat the melt bath; the hot exhaust gases produced are discharged through an outlet in the roof of the reactor. Experiences from experiments in various parts of the world with melt reduction of concentrate in a melt bath have shown that the wear of the tile lining in an area above and a little below the surface of the melt bath is a big problem. In post-combustion above the slag surface, jets of preheated air or, for instance pure oxygen gas, is supplied in such a way that a vigorous agitation of the slag is brought about. Slag drops containing, inter alia, a high content of FeO are caused to splash up into the gas phase in the post-reduction zone. As intended, this results in a very good heat exchange between hot combustion gases and slag drops. At the same time, however, a large amount of slag drops with a high content of FeO will be thrown upwards and outwards and hit the lining in the roof and the walls of the converter. The drops, the temperature of which, due to the combustion, is considerably higher than the melt bath, cause wear and destruction of the lining, and consequently, severe damage. The wear may, if it comes to the worst, be as high as 1,5 mm/h during the process, which would mean a working life of the lining of the converter of only 1200 hours. In order to prevent wear and damage, the use of cooled walls in the converters has been proposed. Converters built entirely of water-cooled panels and converters in which the tile lining has been provided with channels for cooling gas have, for instance, been used. Cooling of the whole converter, the roof as well as the walls, results, however, in high heat losses, which have to be compensated. It is an object of the present invention to provide an improvement of the melt reduction process and apparatus described above. It is a particular object of the invention to reduce the wear and improve the durability of reactors such as converters in melt reduction processes. It is a further object of the invention to provide a melt reduction process in which higher temperatures than earlier can be allowed in the post-combustion zone. The method according to the invention is characterized in that oxygen-containing gas is blown into a post-combustion zone in the converter, which zone is shielded from the walls of the reactor by cooled panels so as to prevent the slag and metal drops splashing up during the blowing from reaching the uncooled walls of the reactor in the gas phase. The apparatus for producing iron by melt reduction of concentrate is characterized in that a shield made of cooled panels is arranged to shield the post-combustion zone from the tile walls of the reactor or corresponding means in an area between the slag layer and the outlet for exhaust gases. According to the invention, the post-combustion takes place in a space shielded by cooled panels from the remaining parts of the reactor. The panel or panels prevent hot molten drops, which splash up into the gas phase in the post-combustion stage, from reaching the tile walls of the reactor. The panel, which may be, for instance, water-, gas- or steam-cooled, endures the wear of these drops considerably better than the uncooled tile wall. The panel can be provided with a heat-insulating layer on its outside in order to prevent unnecessary cooling in the remaining part of the reactor. In most cases a protecting layer of solidified drops is anyhow formed on the panels. The cooled panel is preferably shaped as an upright cylinder disposed concentrically between the surface of the slag and the gas outlet. The cylinder surrounds thereby the post-combustion zone of the reactor. The cooled panel can, if needed, be widened at its upper or lower end so that the shielded zone takes the form of a frustum of cone. When air is used in the post-combustion stage, the gas volumes can be so large that it is advantageous to widen the space shielded by the panels at its lower end. The shield can have a square, rectangular or, for instance, hexagonal cross section. The shield is thus formed of plane water-cooled panels or membrane walls, which is an advantage in the manufacturing stage. The cooled panels are preferably fastened to the roof of the reactor. If needed, openings can be provided in the upper part of the panels or between the panels and the roof of the reactor so that also gases produced outside the shielded part can flow to the gas outlet. Possibly these gases could be withdrawn from the reactor through a separate gas outlet. The lower edge of the cooled panels can in certain cases be allowed to reach the slag surface. A gap between the slag surface and the panels or the openings in the lower parts of the panels allows the gases to flow, if necessary, from the space outside the post-combustion zone via the shielded zone to the gas outlet. When the invention is used in processes with prereduction and partial smelting of the supplied concentrate in a flame chamber made of cooled panels and located above the melt bath reactor, the lower part of the cooled panel walls of the flame chamber can easily be made longer so as to wholly or partly reach the slag surface in the reactor. The post-combustion zone can then be extended to the lower part of the flame chamber. In the process mentioned above, the oxygen-containing gas required in the post-combustion stage is preferably introduced tangentially into the converter by means of one or several blowpipes so that the hot gases flowing upwards form a vortex in the shielded part of the reactor already, thereby promoting the formation of a vortex in the flame chamber. The invention will be described more in detail below with reference to the accompanying drawing, the single figure of which schematically illustrates a plant for melt reduction of iron concentrate according to the invention. The illustrated plant comprises a converter 10 for melt reduction of prereduced molten concentrate. The converter is internally lined with tiles 11. The gas outlet 12 of the converter is connected to a flame chamber 14 for prereduction and smelting of concentrate. The flame chamber is provided with water-cooled membrane walls 15. A reactor 16 having e.g. a fluidized bed is disposed on top of the flame chamber in order to preheat the concentrate. Concentrate is introduced into the reactor chamber 17 of the reactor 16 through an inlet 18. Hot gases from the flame chamber are fed through an opening 20 into the bottom of the reactor. The concentrate is preheated by the exhaust gases in the reactor chamber and flows entrained by the upwards flowing gases via the upper part of the reactor to a particle separator 22. A portion of the preheated concentrate is recycled to the reactor chamber whereas another portion is passed to the flame chamber through a channel 24. Carbonaceous reducing agent 26 is at the same time introduced into the flame chamber. The preheated concentrate is prereduced and smelts in the flame chamber and flows down to the converter for final reduction of the iron oxide in the melt bath 28, 30 of the converter. The melt bath consists of a iron layer 28 on the bottom of the converter and a slag layer 30 on top of the iron layer. Coal 32 and hot blast air 34 is introduced into the converter through openings in the bottom of the converter. Iron and slag is withdrawn through an outlet 36 in the side of the converter. In order to increase the heat transfer to the melt bath, oxygen-containing gas, such as hot blast air, is introduced into a post-combustion zone 37 through blow¬ pipes 38 disposed above the surface 40 of the slag. The blast air is blown in tangentially by the blowpipes so that upwards flowing gases form a vortex and thereby promote the formation of a vortex in the flame chamber. The blast air brings about a vigorous turbulence in the slag layer while the reducing gases are combusted developing heat. The vigorous turbulence results in a good heat transfer in the post-combustion zone between the gas phase and the slag and metal drops splashing up. According to the invention, the post-combustion zone in the converter is shielded by cooled panels 42. The panels have been formed by extending the cooled walls 15 of the flame chamber downward into the converter. In the process illustrated in the figure, the final reduction is effected by means of carbon dissolved in the metal layer. Hot blast air is used for the post-combustion which supplies energy to the slag layer 30 as well as the metal layer 28. The slag layer is thin in comparison with the iron layer. Other corresponding melt bath processes can use oxygen gas in a post-combustion stage, have a considerably thicker slag layer than iron layer and inject the whole amount of coal from above into the gas phase or the slag layer. In these processes the post-combustion supplies energy primarily to the expanding slag layer. Reduction is achieved by means of coke particles and iron drops suspended in the slag. The use of air for post-combustion results, due to the high content of nitrogen in the air, in a lesser reoxidation of iron in comparison with processes using pure oxygen gas. 70% of the oxygen is utilized in processes which use air, whereas only 40 % of the oxygen is used in processes which use oxygen gas. Additionally, the use of air tends to dampen the formation of foam in the slag layer, which is an advantage. As the air furthermore brings about a considerably more vigorous turbulence in the slag layer, the use of air results in an intimate contact between the gas and slag phases. The use of shielded cooled surfaces around the post-combustion zone renders it possible to utilize the above mentioned vigorous turbulence in the converter. The invention is not intended to be restricted to the above described and illustrated embodiment, in which the invention primarily is described in connection with melt reduction in a process with prereduction in a flame chamber. The invention can as well be used in various converter processes. The invention can be modified in many ways within the scope of the inventive idea defined in the appended claims.

Claims: CLAIMS 1. Method for producing iron by melt reduction of concentrate or prereduced concentrate in a melt bath in a reactor, e.g. a converter, wherein concentrate or prereduced and partially molten concentrate and carbonaceous reducing agent, such as coal, is supplied to the melt bath consisting of a layer of molten iron and a layer of slag floating thereon; - oxygen-containing gas, such as hot air, is blown into a so-called post-combustion zone by one or several blowpipes towards the slag layer so as to bring about combustion of the reduction gases being discharged and to heat the melt bath, - the hot exhaust gases produced are discharged through an outlet in the roof of the reactor, characterized in that the oxygen-containing gas is blown into the converter to a post-combustion zone which is shielded from the walls of the reactor by cooled panels so as to prevent the slag and metal drops splashing up during the blowing from reaching the uncooled walls of the reactor in the gas phase. 2. Method according to claim 1, characterized in that concentrate is introduced into the rector via a flash chamber disposed concentrically above the outlet opening for exhaust gas, the exhaust gases from the reactor being passed to the flame chamber for at least partial smelting and prereduction of the concentrate in the flame chamber. 3. Method according to claim 2, characterized in that hot oxygen-containing gas is blown in tangentially so that the exhaust gases form an upward vortex in the post-combustion zone and the flame chamber. 4. Method according to claim 2, characterized in that the exhaust gases from the flame chamber are passed to a reactor disposed above the flame chamber in order to preheat concentrate to be fed into the flash chamber. 5. Method according to claim 1, characterized in that the post-combustion zone is shielded from the walls of the reactor by means of water-cooled panels. 6. Apparatus for producing iron by melt reduction of concentrate or prereduced concentrate in a melt bath in a reactor, e.g. a converter (10) , the melt bath consisting of a layer (28) of molten iron and a layer (30) of slag floating thereon, and the reactor comprising - one or several inlets for concentrate or prereduced and partially molten concentrate and one or several inlets for a carbonaceous reducing agent such as coal, - one or several hot gas blowpipes (38) for introducing oxygen-containing gas, such as hot gas, into a so-called post-combustion zone in the reactor above the surface (40) of the slag so as to bring about combustion of the reduction gases being discharged and heating of the melt bath, and - at least one gas outlet (12) for the hot exhaust gases produced in the post-combustion process located in the roof of the reactor above the post-combustion zone, characterized in that - a shield made of cooled panels (42) is arranged to shield the post-combustion zone (37) from the tile walls (11) of the reactor in an area between the slag layer (30) and the outlet (12) for exhaust gases. 7. Apparatus according to claim 6, characterized in that the shield is formed of an upright cylindrical panel surface (42) disposed concentrically with the gas outlet (12). 8. Apparatus according to claim 6, characterized in that the shield is formed of a panel surface which takes the form of a frustum of cone and is disposed concentrically with the gas outlet. 9. Apparatus according to claim 6, characterized in that the shield is formed of plane panel surfaces. 10. Apparatus according to claim 6, characterized in that the upper part of the shield is disposed around the gas outlet (12) in the roof of the reactor. 11. Apparatus according to claim 6, characterized in that the lower part of the shield reaches the surface (40) of the slag.

Inventors: ELVANDER HANS, MALMSTROEM ROLF, ELVANDER, HANS, MALMSTROEM, ROLF
Applicants: AHLSTROEM OY, ELVANDER HANS, MALMSTROEM ROLF, A. AHLSTROM CORPORATION, ELVANDER, HANS, MALMSTROEM, ROLF
Application year: 1994
Main classification: C21B11
IPC codes: C21B11, C21B13, F27B1, F27B3, F27D17